Summary of Work: Phenolphthalein, a constituent in many laxatives, showed clear evidence of carcinogenic activity in 2-year feeding studies in rodents recently completed by the National Toxicology Program (NTP). About 3% of the older U.S. population uses phenolphthalein-containing laxatives on a daily basis. We will investigate the relation of phenolphthalein-containing laxative use with risk of ovarian cancer and adenomatous colorectal polyps in humans. We have established collaborative agreements with the principal investigators for two ongoing case-control studies of risk factors for ovarian cancer. At our instigation, these investigators have inserted into their questionnaire a 2-page addition that ascertains use of specific phenolphthalein-containing laxatives. Each study will yield about 300 cases and 300 controls, and the data will be ready for analysis in 1999. Data collection for two case-control studies of risk factors for adenomatous colorectal polyps have been completed. Data on laxative use were available for both studies. We have examined laxative use in relation to risk of polyps in these data. The association of polyps with use of all laxatives and phenolphthalein-containing laxatives was specifically explored after taking into account dietary and other risk factors for colorectal adenomas. Results from the two studies were inconsistent with each other but overall offered little support for an association between phenolphthalein-containing laxative use and risk of polyps.